This is a single-center, randomized, participant-blinded, sham-controlled pilot trial designed to evaluate the adjunctive effect of transcutaneous auricular vagus nerve stimulation (taVNS) in overweight or obese patients who show a suboptimal weight-loss response to incretin receptor agonist therapy. A total of 24 participants will be randomly assigned to receive either taVNS plus tirzepatide 5 mg or sham stimulation plus tirzepatide 5 mg for 12 weeks. The primary objective is to compare the percent change in body weight from baseline to week 12 between the two groups.

This is a prospective, single-center, randomized, participant-blinded, sham-controlled, parallel-group pilot study conducted at the Department of Endocrinology, Nanjing Drum Tower Hospital. The study will enroll 24 overweight or obese participants with a suboptimal weight-loss response, defined as a body weight reduction of no more than 10% after at least 24 weeks of incretin receptor agonist treatment. Eligible participants will be randomized in a 1:1 ratio to the taVNS plus tirzepatide 5 mg group or the sham stimulation plus tirzepatide 5 mg group for 12 weeks.

Before and after intervention, all participants will undergo standardized assessments, including lifestyle questionnaires, anthropometric measurements, body composition analysis, autonomic function evaluation, laboratory testing, and assessment of hepatic steatosis and fibrosis. Autonomic function assessment will include heart rate variability, cardiovascular autonomic reflex tests, sudomotor function, and brain MRI. Liver-related assessments will include FibroTouch and liver MRI. During follow-up, body weight will be monitored weekly by telephone or WeChat, waist circumference, hip circumference, and body composition will be reassessed every 4 weeks, and device use will be monitored through an app to ensure adherence and protocol consistency.

The primary endpoint is the between-group difference in percent change in body weight from baseline to week 12. Secondary endpoints include changes in body composition and fat distribution, glucose- and lipid-related metabolic parameters, liver function and hepatic steatosis/fibrosis-related parameters, and autonomic function measures. Exploratory analyses will evaluate changes in brain imaging phenotypes after 12 weeks of intervention.

Inclusion Criteria:

1. Individuals with obesity, or overweight accompanied by at least one weight-related comorbidity (e.g., hypertension or fatty liver disease), who have been receiving incretin receptor agonist therapy for at least 6 months and have achieved ≤10% weight loss during treatment;
2. Willingness to provide written informed consent.

Exclusion Criteria:

1. Presence of diseases that may substantially affect body weight homeostasis, including Cushing's syndrome, uncontrolled thyroid disease (thyroid-stimulating hormone >6.0 mIU/L or <0.4 mIU/L), malignancy, or similar conditions;
2. Use within the past 3 months of medications, other than incretin receptor agonists, that may significantly affect body weight, including glucocorticoids and antipsychotic agents;
3. Skin infection or damage involving the auricular area;
4. Women planning pregnancy in the near future;
5. Contraindications to MRI, such as metallic prostheses or claustrophobia;
6. Diagnosis of diabetes mellitus; Inability to complete the 12-week intervention period for practical reasons, such as frequent business travel or planned travel.

Only participants are masked in this trial. Participants are randomly assigned to active taVNS plus tirzepatide 5 mg or sham stimulation plus tirzepatide 5 mg. To maintain masking, sham stimulation uses the same device, similar stimulation procedures, and the same treatment schedule as active stimulation, but is applied to a non-vagal auricular site (the left tail of the helix). Randomization codes are generated by an independent unblinded team and allocation is concealed using sealed, opaque envelopes. Emergency unblinding materials are prepared and securely retained.